Oxide-semiconductor structures are the major workhorse of the Si semiconductor industry. The requirements for gate quality insulator-semiconductor structures are manifold: (i) low interface state density, e.g. D.sub.it &lt;10.sup.11 cm.sup.-2 ev.sup.-1 ; (ii) low trap density, e.g. N.sub.t .ltoreq.low 10.sup.11 cm.sup.-2, in the insulating film; (iii) thermodynamic interface and insulator stability; and (iv) interface and insulator reliability in particular related to insulator damage caused by injection of (hot) carriers. So far, the only systems which satisfy all of the above outlined specifications is thermal SiO.sub.2 --Si, jet vapor deposited (JVD) Si.sub.3 N.sub.4 --Si, and JVD Si.sub.3 N.sub.4 --SiO.sub.2 --Si.
For Si technology, prior art, for instance A. Malik et al., J. Appl. Phys., 79, 8507 (1996), describes the use of supersonic gas jets for the fabrication of insulating, gate quality silicon nitride films with low N.sub.t on Si. Jet vapor deposition (JVD) uses a supersonic free jet of inert carrier gas to transport vapor species generated from evaporation sources to the surface of a substrate. The quality of silicon nitride films produced by JVD was mainly attributed to a high dissociation efficiency of N.sub.2 (up to 60%) in the supersonic beam using an RF discharge source, see for instance, J. E. Pollard, Rev. Sci.Instrum., vol. 63, 1771 (1992), the small fraction of generated ions, and the absence of H in the silicon nitride films. Some effects of high speed gas dynamics and chemical reactions involved are still under discussion. The technique has been particularly applied for rapidly growing metal and semiconducting films on substrates, see for instance, U.S. Pat. No. 4,788,082, entitled "Method and Apparatus for the deposition of Solid Films of a Material from a Jet Stream Entraining the gaseous phase of Said Material", issued Nov. 29, 1988; U.S. Pat. No. 5,164,040, entitled "Method and Apparatus for Rapidly Growing Films on Substrates Using Pulsed Supersonic Jets", issued Nov. 17, 1992, and U.S. Pat. No. 5,356,673, entitled "Evaporation System and Method for Gas Jet Deposition of Thin Film Materials", issued Oct. 18, 1994. Prior art also includes plasma assisted supersonic gas jets, see for instance, U.S. Pat. No. 5,256,205, entitled "Microwave Plasma Assisted Gas Jet Deposition of Thin Film Materials", issued Oct. 26, 1993, U.S. Pat. No. 5,356,672 entitled "Method for Microwave Plasma Assisted Supersonic Gas Jet Deposition of Thin Films, issued Oct. 18, 1994; and pulsed supersonic gas jets, see for instance, U.S. Pat. No. 5,164,040, entitled "Method and Apparatus for Rapidly Growing Films on Substrates Using Pulsed Supersonic Jets", issued Nov. 17, 1992, U.S. Pat. No. 5,330,610, entitled "Method of Digital Epitaxy by Externally Controlled Closed Loop Feedback, issued Jul. 19, 1994, and U.S. Pat. No. 5,540,783, entitled "Apparatus for Externally Controlled Closed Loop Feedback Digital Epitaxy", issued Jul. 30, 1996.
For compound semiconductors, a low interface state density Dit of 2.5.times.10.sup.10 cm.sup.-2 ev.sup.-1 and full accessibility of the GaAs band gap were demonstrated. Pivotal fabrication aspects include (i) an extremely low GaAs surface exposure to impurities (&lt;10-100 Langmuirs) prior to deposition of the insulating film, and (ii) the preservation of GaAs bulk and surface stoichiometry and the complete exclusion of GaAs surface oxidation. Satisfying the latter requirements and using in-situ deposition of specific molecules (Ga.sub.2 O.sub.3) on GaAs based semiconductor epitaxial layers while maintaining ultra-high vacuum (UHV), resulted in low, D.sub.it interfaces. The GaAs surface exposure (predominantly oxygen) prior to completion of the first Ga.sub.2 O.sub.3 monolayer was typically less than 10 Langmuirs, GaAs surface oxidation was excluded, and GaAs surface stoichiometry preserved. Also, thermodynamic interface stability was demonstrated. See for instance, U.S. Pat. No. 5,451,548 entitled "Electron beam deposition of gallium oxide thin films using a single purity crystal source", issued Sep. 19, 1995, M. Passlack et al., Appl. Phys. Lett., vol. 68, 1099 (1996), Appl. Phys. Lett., vol. 68, 3605 (1996), and Appl. Phys. Lett., vol. 69, 302 (1996).
For compound semiconductors, the remaining problems are associated with stability and reliability issues including charge trapping, carrier injection, and eventually, oxide degradation and breakdown. Trap densities as high as 2.times.10.sup.12 cm.sup.-2 have been found in e-beam deposited Ga.sub.2 O.sub.3 films causing long term drift of device parameters in accumulation and inversion. Consequently, the performance of unipolar and bipolar devices is affected and the fabrication of stable and reliable MOSFETs based on compound semiconductors has been impossible.
Accordingly, it would be highly desirable to provide new methods of manufacturing which overcome these problems.
It is a purpose of the present invention to provide a new and improved method of manufacturing a gate quality oxide-compound semiconductor structure.
It is another purpose of the present invention to provide a new and improved method of manufacturing a gate quality Ga.sub.2 O.sub.3 -compound semiconductor structure.
It is still another purpose of the present invention to provide a new and improved method of manufacturing a gate quality Ga.sub.2 O.sub.3 -compound semiconductor structure with oxide trap density.ltoreq.10.sup.11 cm.sup.-2.
It is a further purpose of the present invention to provide a new and improved method of manufacturing a gate quality Ga.sub.2 O.sub.3 -compound semiconductor structure with oxide trap density.ltoreq.10 .sup.11 cm.sup.-2 and interface state density.ltoreq.10.sup.11 eV.sup.-1 cm.sup.-2.
It is still a further purpose of the present invention to provide a new and improved method of manufacturing a gate quality oxide-compound semiconductor structure with improved stability and reliability.
It is yet a further purpose of the present invention to provide a new and improved method of manufacturing a gate quality oxide-compound semiconductor structure which allows the implementation of stable, reliable, and manufacturable accumulation and/or inversion mode devices using compound semiconductors.
It is still a further purpose of the present invention to provide a new and improved method of manufacturing a gate quality Ga.sub.2 O.sub.3 -compound semiconductor structure which is relatively easy to fabricate and use.